Chart drive mechanism

ABSTRACT

A chart paper drive mechanism is provided in which the chart paper is driven by a pair of drive roller cartridges the rollers of which engage the chart paper near the edges thereof. Each drive roller cartridge is provided with its own friction clutch mechanism which may be independently adjusted to give a desired value of torque at which the drive roller will slip. By equalizing the preset torque of each cartridge the chart paper is driven in a uniform manner and any tendency to skew or weave is rapidly corrected. Also, the cartridges may be readily adjusted to different positions on the drive shaft to accommodate different widths of chart paper.

I United States Patent 1 13,552,62l

72] Inventor Albert Kupfe schmi l 2,857.750 /1958 Fox .1 64/30(C) Chicago, lll. 2,913,885 11/1959 Debrie.. 64/30(C) [21] A 1.No. 757,016 3,092,983 6/1963 Huber 64/30(C) [22] Filed Sept. 3,1968 3,237,830 3/1966 Oswald et a1. 226/174(X) Patented Jan. 5,1971 Prim E N K 1 y xammer en now cs [73 1 Ass'gnee Beckman q' Attorneys- Richard M. Jennings and Robert J. Steinmeyer a corporatlon oi Callfornla I54] a y M' g'Z ABSTRACT: A chart paper drive mechanism is provided in rawmg g which the chart paper is driven by a pair of drive roller car- U.S. {ridges the rollers of which engage the han paper near the 226/l74 edges thereof. Each drive roller cartridge is provided with its [51] Int. Cl Bh 17/20 own f iction l h mechanism which may be independently [50] Field ofSearch 226/174, adjusted to give a desired value of torque at which the drive I 37, 188;64/30C roller will slip. By equalizing the preset torque of each cartridge the chart paper is driven in a uniform manner and any References Cned tendency to skew or weave is rapidly corrected. Also, the car- UNITED STATES PATENTS tridges may be readily adjusted to different positions on the 2,274,834 3/1942 lra 226/187 drive shaft t acc mm dat different idth of hart p p r- 56:: 40 580 g m V f. V i. 20,

56d44/(64 '-r- 58a PATENTED JAN SIS?! 3,552,621

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.[ O l l IN VENTOR ALBERT KUPFERSCHM/DT Attorney CHART DRIVE MECHANISM The present invention relates to drive mechanisms, and, more particularly, to chart drive mechanisms suitable for use in chart recorders to drive the chart paper of the recorder in a uniform manner.

Various arrangements have been heretofore proposed for obtaining a uniform drive or feed of the continuous web or strip of paper normally used in chart recorders. One such arrangement is shown in Offner U.S. Pat. No. 2,977,l 12 wherein a plurality of roller sections are employed across the entire width of the chart, these roller sections being loaded against one another through friction washers by pressure exerted on one end of the drive roller assembly. While the arrangement shown in Offner U.S. Pat. No. 2,977,l 12 provides some measure of correction for skewing of the chart paper, such correction is necessarily incomplete and slow acting due to the fact that the roller sections nearest the end at which pressure is applied do not have the same slipping torque as the roller sections at the far end of the roller unit. Furthermore, the arrangement shown in Offner U.S. Pat. No. 2,977,112 has the further disadvantage that it cannot readily be adapted to function with different widths of chart paper.

It is, therefore, a primary object of the present invention to provide a new and improved chart drive mechanism which is simple and economical to manufacture and which avoids one or more of the difficulties of the prior art arrangements discussed heretofore.

It is another object of the present invention to provide a new and improved chart drive mechanism wherein the chart paper is driven by a single pair of drive roller units positioned near the edges of the chart paper and skewing or weaving of the paper as it is driven is rapidly corrected.

It is a further object of the present invention to provide a new and improved chart drive mechanism in which the chart paper is driven by a pair of drive roller units in engagement with the paper near the edges thereof, the drive rollers of each unit being adapted to slip at the same predetermined value of torque so that skewing of the paper is rapidly and positively corrected.

It is a still further object of the present invention to provide a new and improved chart drive mechanism in which the chart paper is driven by a pair of drive roller units positioned on a transverse drive shaft and in engagement with the chart paper near the edges thereof, at least one of said drive roller units being adjustably positionable along the length of said drive shaft to accommodate charts of different widths in a simple and economical manner.

Briefly, in accordance with one aspect of the invention, a pair of drive roller units are separately and independently mounted on the transverse roller drive shaft of the chart recorder, these drive roller units being positioned to engage the chart paper near the edges thereof. Each of the drive roller units is provided with a friction clutch arrangement which can be accurately set to the desired torque value. Furthermore, each of these units may be adjustably positioned at different points along the drive shaft so that chart paper of different widths can be used with very slight modification of the mechanism.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing in which:

FIG. 1 is a top plan view of a chart drive mechanism embodying the features of the present invention;

FIG. 2 is a fragmentary sectional view taken along the lines 2-2 of FIG. I;

FIG. 3 is a sectional view taken along the lines 3-3 of FIG. 2; and

FIG. 4 is a fragmentary view similar to FIG. 1 but showing one of the drive roller units in a different adjusted position on the drive shaft.

Referring now to the drawings, and more particularly to FIG. 1 thereof, the chart drive mechanism of the present invention is therein illustrated as comprising a drive shaft 10 which is positioned transversely of the chart paper and is supported at either end thereof by the members I2, I4, the members l2, 14 being spaced from the sidewalls 16, I8 of the recorder by means of spacer blocks 20 and 22. The drive shaft 10 is arranged to be driven from a motor 24, a transmission unit 26, including gears 28 and 30, and a transfer gearing arrangement or speed reduction unit, indicated generally at 32, which is provided with an output bevel gear '34 in engagement with a bevel gear 36 secured to the drive shaft 10 by means of the setscrew 38. The transfer gearing 32 is arranged to provide a selectable speed of rotation of thedrive shaft 10 in accordance with the desired chart paper drive speed for a particular recording operation, as will be readily understood by those skilled in the art.

A pair of drive roller units, or cartridges, 40, 42 are secured to the drive shaft 10 by means ofthe setscrews 44, 46. respectively. In accordance with an important aspect of the inven tion, only two of these drive roller units are employed and the drive rollers of these units are arranged to engage the chart paper near the edges thereof, the drive shaft 10 being driven through the bevel gear 36 at a point intermediate the roller units 44), 42 so that the drive roller units 40, 42 may be positioned out to the ends of the drive shaft 10 to accommodate relatively wide chart paper while providing a minimum width for the overall chart recorder.

Considering now the other portions of the chart drive mechanism whereby chart paper is fed to the drive roller units 40, 42, in the illustrated embodiment folded chart paper I I is stored in a suitable container (not shown) below the illustrated chart drive mechanism, and extends upwardly over a roller 70. The chart paper 11 then extends between a felt pad 72, which extends transversely across the line of travel of the chart paper, and a bar 74, the bar 74 being urged against the felt pad 72 by means of a pair of springs 76 so as to provide a predetermined amount of back tension for the paper supply against which the drive roller units 40, 42 can work. The car chart paper ll then extends upwardly over a guide roller 78 and then over the drive roller units 40, 42. A pair of pressure rollers 80 are rotatably mounted on bell crank levers 82, the levers 82 being pivotally mounted on the sidewalls 16, I8 and being spring biased by means of the springs 84 so that the pressure rollers 80 press the chart paper against the drive rollers of the units 40, 42 with a predetermined force. The bell crank levers 82 are pivotally mounted on the studs 86 and the levers 88 on which the bars 70 and 74 are mounted are pivotally mounted on studs 90. The levers 82 and 88 may conveniently be lifted away from their drive positions to facilitate the loading of chart paper into the drive mechanism, as will be readily understood by those skilled in the art.

Referring now to FIG. 3, the drive roller unit 40 is therein illustrated in more detail a comprising a bushing member 50, which is secured to a flat on the shaft 10 by means of the setscrew 44 and is provided with an enlarged shoulder portion 52. A drive roller 54 is rotatably mounted on the bushing 50 and is positioned between a pair of friction washers 56, 58 which engage the opposite sides of the roller 54. Each of the washers 56, 58 is provided with ear portions 56a and 580, respectively. The ears 56a are adapted to engage the flat sides of the shoulder 52 which may be hexagonal in shape. The ears 58a are adapted to engage or key with the flat sides of a hexagonally shaped nut 60 which is threaded onto the right-hand end of the bushing 50, as viewed in FIG. 3. A bowed spring washer 62 is positioned between the nut 60 and the washer 58 and as the nut 60 is tightened on the bushing 50 a longitudinal compressive force is exerted on the drive roller 54. As a result of such construction, the torque which must be overcome to cause the roller 54 to slip with respect to the bushing 50 may be accurately adjusted to a predetermined value. This torque is the product of the longitudinal compressive force on the drive roller 54 and the coefficient of static friction acting at the mean radius of each interface between the drive roller 54 and the washers 56 and 58. Preferably, the roller 54 is made of steel and the washers 56, 58 are made of a similar material, such as, for example, brass, which will give the desired coefficient of friction with respect to the steel drive roller 54. Preferably, a suitable grease or other lubricant is employed between the washers 56,58 and the roller 54 to minimize wear on the engaging surfaces of these parts. The pressure rollers 80 may have any desired width up to the width of the drive rollers of the units 40, 42. However, it has been found that these pressure rollers 80 need have only setscrew of approximately one-fourth inch to cooperate satisfactorily with drive rollers 54 of five-eights inch width to obtain suitable skew and weave correction for the chart paper.

When the nut 60 has been adjusted to give a desired value of torque for the drive roller unit, this nut is locked in adjusted position by means of a setscrew 64. Since both the bushing 50 and the nut 64 are locked against rotation and since the washers 56 and 58 are provided with the ear portions 56a and 58a which would prevent rotation of these members, the torque which must be exerted on the drive roller 54 may be accurately adjusted to a predetermined value. The tangential force on the roller 54 may range from an ounce or less to several pounds depending on the particular chart drive application, the width and character of the chart paper, and other factors. In accordance with an important feature of the present invention, each of the drive roller units 40, 42 is provided as a separate,'independently adjustable cartridge unit, each of which maybe independently positioned along the length of the drive shaft to accommodate chart papers of different widths. By virtue of the above-described construction of each cartridge unit, the torque required to cause each of the drive roller units to slip may be accurately adjusted to the same value, by adjustment of the nut 60 of each unit, and this adjustment is thereafter accurately maintained in each drive roller cartridge. When two drive roller units are employed, the force which overcomes the preset staticfriction torque of each drive roller cartridgecan theoretically be set to a value slightly more than one-half the back tension of the chart paper 11 so that the combined force of the two units before slipping occurs will be sufficient to pull the chart paper against the back tension thereof. However, it has been found in practice that the preset force of each drive roller unit is preferably set to a value slightly above the back tension of the chart paper so that variations in back tension, coarseness of the chart paper and variations in friction introduced by the intermediate shafts do not cause the drive roller 54 to slip under uniform paper drive conditions. The force at which each drive roller will slip may be set in any desired manner. For example, a piece of leather, simulating the chart paper, may be placed between the pressure roller 80 and the drive roller 54 and the desired force exerted on this piece of leather, as indicated by a suitable spring scale or other measuring device. The nut 60 is then adjusted until the drive roller 54 just starts to slip and is then locked in position by means of the setscrew 64.

Considering now the operation of the drive roller units 40, 42, it is pointed out that because the preset force of each drive roller cartridge can be set to exactly the same value, the correction for any skewing or weaving tendency of the chart paper is almost immediately made with the result that the chart paper is pulled against the back tension in a substantially uniform manner without any substantial degree of skew or weave.

More particularly, when one side of'the paper is tighter than the other. a condition at which skewing or weaving will start, the drive roller 54 on the tight side of the chart paper will see a greater load, since it is pulling the paper entirely by itself at that instant. The static friction torque holding this drive roller will be overcome and it will slip relative to the drive shaft 10. The drive roller 54 on the loose side of the chart paper is still turning with the drive shaft and hence will pick up the slack until the paper is taut across the transverse line which the two drive roller units make with the chart paper. At this time the load is again evenly distributed so that the drive roller units pull the paper together. In order to illustrate one example of the manner in which the drive roller units may be independently adjusted along the length of the drive shaft 10 to accommodate chart papers of different widths, there is shown in FIG. 4 a repositioning of the drive roller unit 40 to accom modate a different width of chart paper.

In the arrangement shown in FIG. 1, the drive roller units 40, 42 have been illustrated as adjusted to a position suitable for driving eight-channel chart paper for cooperation with a particular recording mechanism. However, in the arrangement shown in FIG. 4, the spacer blocks 20, 22 have been removed and the drive roller cartridge units 40, 42 have been moved outwardly to a position near the outer ends of the drive shaft 10 so as to accommodate ten-channel chart paper. In I chart paper of the present invention to different widths of chart paper is extremely simple and may be readily made by the user of the equipment in the field. In this connection, while a change from 8 /2 inch chart paper to 10 /2 inch chart paper has been illustrated, it will be understood that much larger differences in chart paper widths may be accommodated in accordance with the chart paper mechanism of the present in vention. Thus, a chart drive mechanism arranged to drive 16- inch chart paper maybe readily changed to drive l2inch chart paper, 8-inch chart paper, or even 4-inch chart paper, by suitable adjustment of the drive roller units 40, 42.

While there have been illustrated and described various cmbodiments of the present invention, it will be apparent that various changes and modifications thereof will occur to those skilled in the art. It is intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the present invention.

I claim:

1. In a chart drive mechanism for pulling chart paper against a predetermined back tension, a combination for automatically correcting skew or weaving of the chart paper comprising a rotatable drive shaft positioned transversely of said chart paper, a pair of drive roller units positioned on said drive shaft at points which are spaced apart along the length thereof, each of said drive roller units including a bushing secured to said drive shaft and rotatable therewith, a drive roller rotatably mounted on said bushing, friction clutch means interconnecting said drive roller with said bushing so that a predetermined torque must be exerted on the periphery of said drive roller to cause said drive roller to slip relative to said bearing, and means for independently adjusting the predetermined torque exerted on the periphery of each drive roller, each drive roller unit being set to slip at the same torque.

2. In a chart recorder, a combination for automatically correcting skew or weaving of the chart paper comprising a drive shaft, a pair of drive roller units secured to said drive shaft at spaced points thereon, said units each having a drive roller adapted to engage the chart in anarea near the edge thereof, means for urging said areas of the chart into engagement with said drive rollers of said units, and friction clutch means in each unit being set to permit said drive roller of the associated unit to slip at the same predetermined value of torque, whereby said pair of drive rollers drive the chart without introducing skewing or weaving thereof.

3. In a chart recorder as claimed in claim 2, wherein at least one of the drive roller units may be selectively moved along the drive shaft to vary the space between the drive roller units so as to accommodate chart paper of different widths.

4. In a chart recorder as claimed in claim 2, wherein the' combination includes two drive roller units only, one drive roller unit disposed at each edge of said chart paper. 

1. In a chart drive mechanism for pulling chart paper against a predetermined back tension, a combination for automatically correcting skew or weaving of the chart paper comprising a rotatable drive shaft positioned transversely of said chart paper, a pair of drive roller units positioned on said drive shaft at points which are spaced apart along the length thereof, each of said drive roller units including a bushing secured to said drive shaft and rotatable therewith, a drive roller rotatably mounted on said bushing, friction clutch means interconnecting said drive roller with said bushing so that a predetermined torque must be exerted on the periphery of said drive roller to cause said drive roller to slip relative to said bearing, and means for independently adjusting the predetermined torque exerted on the periphery of each drive roller, each drive roller unit being set to slip at the same torque.
 2. In a chart recorder, a combination for automatically correcting skew or weaving of the chart paper comprising a drive shaft, a pair of drive roller units secured to said drive shaft at spaced points thereon, said units each having a drive roller adapted to engage the chart in an area near the edge thereof, means for urging said areas of the chart into engagement with said drive rollers of said units, and friction clutch means in each unit being set to permit said drive roller of the associated unit to slip at the same predetermined value of torque, whereby said pair of drive rollers drive the chart without introducing skewing or weaving thereof.
 3. In a chart recorder as claimed in claim 2, wherein at least one of the drive roller units may be selectively moved along the drive shaft to vary the space between the drive roller units so as to accommodate chart paper of different widths.
 4. In a chart recorder as claimed in claim 2, wherein the combination includes two drive roller units only, one drive roller unit disposed at each edge of said chart paper. 